[llvm] r256338 - [SCEV] Fix getLoopBackedgeTakenCounts

[Sanjoy Das via llvm-commits]

Author: sanjoy
Date: Wed Dec 23 11:48:14 2015
New Revision: 256338

URL: http://llvm.org/viewvc/llvm-project?rev=256338&view=rev
Log:
[SCEV] Fix getLoopBackedgeTakenCounts

The way `getLoopBackedgeTakenCounts` is written right now isn't
correct. It will try to compute and store the BE counts of a Loop
 #{child loop} number of times (which may be zero).

Modified:
    llvm/trunk/lib/Analysis/ScalarEvolution.cpp

Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=256338&r1=256337&r2=256338&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Wed Dec 23 11:48:14 2015
@@ -9439,23 +9439,22 @@ static void replaceSubString(std::string
 /// getLoopBackedgeTakenCounts - Helper method for verifyAnalysis.
 static void
 getLoopBackedgeTakenCounts(Loop *L, VerifyMap &Map, ScalarEvolution &SE) {
-  for (Loop::reverse_iterator I = L->rbegin(), E = L->rend(); I != E; ++I) {
-    getLoopBackedgeTakenCounts(*I, Map, SE); // recurse.
+  std::string &S = Map[L];
+  if (S.empty()) {
+    raw_string_ostream OS(S);
+    SE.getBackedgeTakenCount(L)->print(OS);
 
-    std::string &S = Map[L];
-    if (S.empty()) {
-      raw_string_ostream OS(S);
-      SE.getBackedgeTakenCount(L)->print(OS);
-
-      // false and 0 are semantically equivalent. This can happen in dead loops.
-      replaceSubString(OS.str(), "false", "0");
-      // Remove wrap flags, their use in SCEV is highly fragile.
-      // FIXME: Remove this when SCEV gets smarter about them.
-      replaceSubString(OS.str(), "<nw>", "");
-      replaceSubString(OS.str(), "<nsw>", "");
-      replaceSubString(OS.str(), "<nuw>", "");
-    }
+    // false and 0 are semantically equivalent. This can happen in dead loops.
+    replaceSubString(OS.str(), "false", "0");
+    // Remove wrap flags, their use in SCEV is highly fragile.
+    // FIXME: Remove this when SCEV gets smarter about them.
+    replaceSubString(OS.str(), "<nw>", "");
+    replaceSubString(OS.str(), "<nsw>", "");
+    replaceSubString(OS.str(), "<nuw>", "");
   }
+
+  for (auto *L : reverse(*L))
+    getLoopBackedgeTakenCounts(L, Map, SE); // recurse.
 }
 
 void ScalarEvolution::verify() const {